arm64: dts: rockchip: fix pinmux of UART5 for PX30 Ringneck on Haikou

UART5 uses GPIO0_B5 as UART RTS but muxed in its GPIO function,
therefore UART5 must request this pin to be muxed in that function, so
let's do that.

Fixes: 5963d97 ("arm64: dts: rockchip: add rs485 support on uart5 of px30-ringneck-haikou")
Cc: stable@vger.kernel.org
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Link: https://lore.kernel.org/r/20250225-ringneck-dtbos-v3-2-853a9a6dd597@cherry.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Author: QSchulz

arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts

@@ -194,6 +194,13 @@
 			  <3 RK_PB3 RK_FUNC_GPIO &pcfg_pull_none>;
 		};
 	};
+
+	uart {
+		uart5_rts_pin: uart5-rts-pin {
+			rockchip,pins =
+			  <0 RK_PB5 RK_FUNC_GPIO &pcfg_pull_none>;
+		};
+	};
 };
 
 &pwm0 {
@@ -228,6 +235,9 @@
 };
 
 &uart5 {
+	/* Add pinmux for rts-gpios (uart5_rts_pin) */
+	pinctrl-names = "default";
+	pinctrl-0 = <&uart5_xfer &uart5_rts_pin>;
 	rts-gpios = <&gpio0 RK_PB5 GPIO_ACTIVE_HIGH>;
 	status = "okay";
 };